German Patent No. 35 19 437 and German Patent No. 37 34 274 have disclosed methods for manufacturing a pin heater from composite materials on the basis of trisilicon tetranitride (Si.sub.3 N.sub.4) and molybdenum silicide (MoSi.sub.2) using an axial hot pressing technique, with separate sintered-in power supply wires. The complex construction and laborious manufacturing method of these pin heaters, in which green machining of the pin (before sintering) is not possible, but rather only hard machining with diamond tools after sintering is possible, are regarded as disadvantageous.
European Patent No. 0 721 925 describes a method for manufacturing a dense silicon nitride composite material. Although this material is temperature-resistant, electrically conductive composites cannot be created using the manufacturing method.
European Patent No. 0 601 727 describes a method for manufacturing a pin heater from Si.sub.3 N.sub.4 /MoSi.sub.2 composites. It can be manufactured by hot pressing or sintering under 10.sup.5 Pa of nitrogen at 1600.degree. C. The composite material only begins to sinter at this temperature, resulting in relatively low strength values. This strength level is not sufficient for utilization of the pin heater, for example as a diesel starting aid. Complete sintering of the composite ceramic described is not possible under the manufacturing conditions indicated in European Patent No. 0 601 727. As a result, gas-tightness of the pins--which must exist if they are used, for example, as glow plugs--is also not ensured.
German Patent Application No. 197 22 321 describes a method for manufacturing a shaped element having adjustable electrical conductivity from a ceramic composite structure that contains at least two constituents of differing electrical conductivity, such as Si.sub.3 N.sub.4 and a metal silicide, the shaped element being produced before sintering by way of a cold isostatic mold pressing step. A method for manufacturing a pin heater is not, however, recited therein.